JPH054274B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a four-wheel steering system for a vehicle that steers the rear wheels in response to the steering of the front wheels. More specifically, the four-wheel steering system includes a controller that issues a command signal to a rear wheel steering mechanism to steer the rear wheels based on a ratio of a rear wheel steering angle to a front wheel steering angle determined in accordance with at least vehicle speed. Regarding equipment.

(Prior art) Conventionally, four-wheeled vehicles were typically steered by turning only the front wheels using a steering wheel.
Problems have been pointed out in terms of maneuverability and steering, such as steering only the front wheels, which may cause sideslip in the rear wheels depending on the driving situation, or limit the turning radius, making it impossible to make small turns. In view of this, four-wheel steering devices that steer both the front wheels and the rear wheels have recently been proposed and researched.

In other words, with a four-wheel steering system, when driving at relatively high speeds, if the rear wheels are steered in the same direction as the front wheels (this is called in-phase steering), lateral forces are applied to the front and rear wheels at the same time. Because of this, there is no phase lag from the steering wheel steering, and the vehicle's attitude can be maintained almost on the tangent to the turning circle, allowing smooth lane changes, for example, when driving at high speeds. Also, if the rear wheels are steered in the opposite direction to the front wheels when driving at very low speeds (this is called reverse phase steering), the direction of the vehicle can be changed significantly, which is convenient for parallel parking or parking in a garage.

Furthermore, considering that the front wheels are not steered significantly at relatively high speeds, and the front wheels are steered significantly when driving at relatively low speeds, the rear wheels are also steered within the range where the front wheels are steered small. steer in the same direction,
When making a large turn, steer the rear wheels in the opposite direction 4
It can be seen that a wheel steering device is required.

For this reason, we have provided a mechanism that can arbitrarily variably control the ratio of the steering angle of the rear wheels to the steering angle of the front wheels, that is, the steering ratio, and adjust the steering ratio according to vehicle speed, front wheel steering angle, etc. It has been proposed to improve maneuverability, driving stability, etc. by variable control of

For example, as disclosed in Japanese Patent Laid-Open No. 59-77968, the steering ratio of the rear wheels relative to the front wheels is controlled by a controller, and this controller is operated based on a vehicle speed signal from a vehicle speed sensor. It has a four-wheel steering system.

In this way, when performing four-wheel steering according to the vehicle speed, the vehicle speed always fluctuates minutely depending on road surface conditions, etc., and the detection signal also varies depending on the accuracy of the vehicle speed sensor that detects the vehicle speed, twisting of the sensor cable, etc. Since the steering ratio fluctuates, there is a problem in that if the steering ratio is controlled in response to these small fluctuations, the rear wheels may wobble or the like, resulting in a loss of stability.

(Object of the Invention) In view of the above-mentioned problems, the present invention provides a four-wheel system for a vehicle in which a vehicle speed signal input to a controller for controlling four-wheel steering is subjected to hysteresis processing to eliminate the adverse effects caused by minute fluctuations in vehicle speed. The object of the present invention is to provide a steering device.

(Structure of the Invention) The four-wheel steering device of the present invention includes a controller that issues a command signal to the rear wheel steering mechanism to variably control the steering ratio according to at least the vehicle speed, and the controller includes a signal processing unit that controls the steering ratio. The present invention is characterized in that a vehicle speed signal obtained by subjecting a signal from a vehicle speed sensor to hysteresis processing is input.

The above-mentioned hysteresis processing means a process in which even if the vehicle speed fluctuates within a certain range, the vehicle speed signal detected by the vehicle speed sensor and used as control information in the controller is maintained at a constant value. For example, when detecting pulses detected from a vehicle speed sensor, the number of pulses (N) is within a _{predetermined} width (±
As long as the speed remains within the variation of α), the first detected number of pulses (N ₁ ) continues to be sent as the vehicle speed signal sent to the controller, and when it fluctuates beyond this predetermined width, the vehicle speed signal sent to the controller is changed for the first time. By performing hysteresis processing in this way, the operation of the controller is not affected by small fluctuations in vehicle speed, and stable control can be performed.

(Examples) Hereinafter, the present invention will be described in detail with reference to examples shown in the drawings.

FIG. 1 is a schematic diagram showing one embodiment of a four-wheel steering system according to the present invention. The steering wheel 1 is connected to a first pinion 2 via a steering shaft 1a, and the first pinion 2 meshes with a rack of a first rack shaft 3 that is slidable in the vehicle width direction. Right and left tie rods 4 are attached to both ends of the first rack shaft 3.
a, 4b are connected, and the tie rods 4a, 4b are connected to arms of knuckles 5a, 5b that support the right and left front wheels 6a with respect to the vehicle body so as to be steerable (note that since the left and right wheels are symmetrical, the left tie rod 4b, the knuckle 5b, The front wheel 6b is not shown). Therefore, the first rack shaft 3 moves in the vehicle width direction in response to the operation of the steering wheel 1, and this movement is transmitted to the knuckles 5a, 5b via the tie rods 4a, 4b, so that the front wheels 6a, 6b are steered.

On the other hand, a second rack shaft 7 parallel to the first rack shaft 3 is integrally connected to the first rack shaft 3 via a connecting portion 7a, and the rack of the second rack shaft 7 has a steering force to be transmitted to the rear wheels. The second pinion 8 is engaged to obtain the following. Therefore, when the first rack shaft 3 is moved in the vehicle width direction, the second rack shaft 7 is simultaneously moved in the same direction, and the second pinion 8 is rotated. The rotation of the second pinion 8 is transmitted to the variable steering ratio rear wheel steering mechanism 10 via the power transmission shaft 9 connected to the second pinion 8, and the rear wheels are rotated according to the steering ratio adjusted here. Be steered. In this way, the rear wheels can be steered in accordance with the front wheels steered.

Next, the variable steering ratio rear wheel steering mechanism 10 will be explained. The rear end of the power transmission shaft 9, whose front end is connected to the second pinion 8, is connected to a third pinion 11, and the third pinion 11 meshes with a bevel gear 12 whose rotating shaft 12b is supported by the vehicle body. A rod support hole 12a is formed at one location on the circumference of the bevel gear 12, and a connecting rod 13 is inserted into the rod support hole 12a so as to be rotatable relative to the bevel gear 12 and slidable in the axial direction of the rod 13. Ru. One end 13a of the rod 13 is connected to a third valve for steering the rear wheels via a control valve 15 for power steering.
Connecting arms 14a, 14 connected to rack shaft 17
Connect with b using a ball joint. The third rack shaft 17 is held in the rear wheel gearbox 16 so as to be slidable in the vehicle body direction, and both ends of the third rack shaft 17 are connected to right and left knuckles 19a and 19b via right and left tie rods 18a and 18b. . Since the right and left knuckles 19a, 19b support the rear wheels 20a, 20b so as to be steerable relative to the vehicle body, the rear wheels are steered by movement of the third rack shaft 17 in the vehicle width direction. Note that the tie rod, nut, and rear wheel are symmetrical, so only the right side is shown. The movement of the third rack shaft 17 in the vehicle width direction is as follows:
The movement of one end 13a of the connecting rod 13 in the vehicle width direction due to the rotation of the bevel gear 12 causes the connecting arm 14a,
14b to the third rack shaft 17. At this time, by the action of the control valve 15 installed on the coupling arms 14a, 14b, pressure oil from the pump 21 is appropriately sent into the cylinder in the rear wheel gearbox 16, and the third rack shaft 1
It is designed to assist the movement of 7.

Next, a mechanism for moving one end 13a of the connecting rod 13 in the vehicle width direction in accordance with the rotation of the bevel gear 12 will be described. The other end 13b of the connecting rod 13
is connected to the tip of the pendulum arm 22 via a ball joint, and this pendulum arm 22 is connected to the tip of the pendulum arm 22 via a ball joint.
2 and a swing shaft 23 perpendicular to the swing shaft 23.
It can be rotated freely around the center. This swing shaft 23
is extended and supported in a horizontal plane by a swinging support shaft 24 extending vertically, and swings in the horizontal plane in response to rotation of the swinging support shaft 24. Since the rotating surface of the pendulum arm 22 is tilted in accordance with the swinging of the swing shaft 23, the rate at which one end 13a of the connecting rod 13 is moved in the vehicle width direction varies in accordance with the rotation of the bevel gear 12.

This operation will be explained using a schematic plan view of the variable steering ratio mechanism shown in FIG. First, the swing axis 2
3 extends in the vehicle width direction and is the rotating shaft 1 of the bevel gear 12.
Consider the case where it is located on the same straight line as 2b. In addition,
One end 13a of the connecting rod 13 is also located on the rotation axis of the bevel gear 12. At this time, bevel gear 1
2 is rotated, the connecting rod 13 has one end 13a
The pendulum arm 22 moves on a conical surface with the apex at the apex and the connecting rod 13 as the ridgeline, and the pendulum arm 22 moves on the bottom surface of this cone. Therefore, even if the bevel gear 9 rotates, the one end 13a does not move. That is, at this time, the rear wheels are not steered while the front wheels are steered. From this state, by rotating the swing support shaft 24 and tilting the swing shaft 23 counterclockwise in the horizontal plane by "" as shown in the figure, the rotating surface of the pendulum arm 22 is aligned "" with respect to the bottom surface of the cone. Just lean. Therefore, for example, if the bevel gear 12 is rotated so that the angle between the connecting rod 13 and the rotating shaft _12b of the bevel gear 12 in FIG. The _first end 13a also moves approximately the same distance to the position 13a'. As a result of this movement, the third rack shaft 17 is similarly moved and the rear wheels are steered. As can be seen from this figure, the ratio of the rear wheel steering angle to the front wheel steering angle, that is, the steering ratio, is the ratio of the rotation of the connecting rod 13 to the rotation of the bevel gear 12.
The amount of movement of the one end 13a is the same as that of the swing shaft 23.
The steering ratio can be changed depending on the magnitude of the inclination "" in the horizontal plane. Furthermore, the swing shaft 23 can be tilted not only counterclockwise as described above, but also clockwise, and in this case, one end 1 of the connecting rod 13 is connected to the rotation of the bevel gear 12.
The moving direction of 3a is opposite to the above case. Thereby, the rear wheels can be steered in the same phase or in the opposite phase with respect to the front wheels.

Next, a mechanism for swinging the swing shaft 23 in a horizontal plane will be explained. The swing shaft 23 extends in a horizontal plane and is supported by a swing support shaft 24 extending vertically, and a swing gear 25 having a gear 25a at the tip is fixed to the swing support shaft 24. , the swing support shaft 24 is rotated by the swing of the swing gear 25 around the swing support shaft 24.
3 is rocked. The gear 25a of the swing gear 25 meshes with a worm 26, and the worm 26 meshes with a first bevel gear 28 provided on the output shaft 29a of the step motor 29 and a first bevel gear 28 provided on the same axis as the worm 26. It is rotated by a step motor 29 via a double bevel gear 27. The rotation of the step motor 29 is controlled by a swing angle sensor 33 provided on the swing support shaft 24 that detects the swing angle of the swing shaft 23 and a vehicle speed sensor 32 that detects the vehicle speed via a hysteresis processing section 34. The step motor drive circuit 30 is controlled based on a control signal sent from the electric controller 31 that receives the detection signal to the step motor drive circuit 30.

The graph in FIG. 3 shows an example of control by the electric controller 31, and in this way, the rear wheel steering angle relative to the steering wheel steering angle (front wheel steering angle), that is, the steering ratio, is changed according to the vehicle speed. ing.
In this example, in a low speed range, the rear wheels are steered in opposite phases to improve turning performance, and in high speed ranges, the rear wheels are steered in the same phase to improve driving stability. In this case, the controller 31 is constituted by an arithmetic processing device such as a microcomputer that performs arithmetic processing according to a preset program. The rear wheel steering mechanism 1 determines the steering angle ratio) and steers the rear wheels based on the steering ratio.
In particular, a command signal is issued to the step motor 29 in the mechanism, and the step motor 29 is driven in a predetermined rotation direction by a predetermined pulse amount based on this signal, and the steering ratio is accordingly changed as shown in FIG. Change.

The vehicle speed signal sent to the controller 31 is
This signal is not the signal itself detected by the vehicle speed sensor 32, but is subjected to hysteresis processing by the hysteresis processing section 34. This hysteresis processing prevents the transmission of minute fluctuations in the vehicle speed and enables stable control. ing. Further, the hysteresis processing section 34 is configured to receive an output from a vehicle speed determination section 35 that receives a signal from the vehicle speed sensor 32 and detects whether or not the actual vehicle speed has become zero. 35 detects that the actual vehicle speed has become zero, a signal is sent from the vehicle speed determination section 35 to the hysteresis processing section 34, and the hysteresis processing section 34 receives this signal and sets the width of the hysteresis processing to zero. . As a result, when the actual vehicle speed is zero, the vehicle speed signal sent to the controller 31 also becomes zero, and the initial setting of the rear wheels can be performed with the vehicle reliably stopped.

In other words, in a four-wheel steering system, when steering ratio control is performed, slight deviations may occur in the position of the rear wheels relative to the front wheels, the steering ratio control system, etc. If left unchecked, the deviation will gradually increase and the steering ratio control will become abnormal, which could impair maneuverability and stability.In general, the position of the rear wheels is detected and feedback control is performed to adjust the position to the correct position. I am trying to perform an initial reset. If this initial set is performed while the vehicle is running, there is a danger that the rear wheels may wobble due to the setting, so the initial set is performed while the vehicle is stopped. However, when hysteresis processing is performed in vehicle speed detection as described above, the detected vehicle speed may be determined to be non-zero even though the actual vehicle speed is zero, or the detected vehicle speed may be determined to be zero even though the actual vehicle speed is not zero. If the initial setting of the rear wheels is performed in such a state, there is a problem that the error in the position of the rear wheels, that is, the steering ratio, may become larger.

Therefore, in this embodiment, when the actual vehicle speed is detected to be zero by the vehicle speed determination section as described above, the width for performing the hysteresis processing is set to zero, and as a result, the width for performing the hysteresis processing is set to zero. Since the control vehicle speed signal becomes zero only when the vehicle comes to a complete stop, the rear wheels can be initialized while the vehicle is completely stopped, and control errors can be reduced.

The control contents of the controller 31 and the hysteresis processing section 34 explained above will be explained using the flowchart of FIG. 4.

The vehicle speed processing routine shown in this flowchart starts at step S1 and ends at step S10, and this routine is interrupted at predetermined intervals.
This interrupt processing interval is determined depending on the type of vehicle speed sensor, etc. In this embodiment, a 20-pulse sensor is used as the vehicle speed sensor, and this sensor rotates 637 times when the car travels 1 km.
The pulse period T when the vehicle speed is 1 Km/H is T = 3600 (seconds) / {1 (Km/H) x 637 (rotations) x 20 (pulses/turns)} = 0.282575 (s), so T = Performs interrupt processing every 0.282575 seconds. As a result, the number of pulses input during this T (seconds) becomes the same as the vehicle speed (Km/H).

When performing the above-mentioned interrupt processing with a period of T (seconds), the number of pulses is “N” and the detected vehicle speed is “V (Km/Km)”.
H)", when the vehicle speed processing routine started at step S1 advances to step S2, the number of pulses N (this value is the number of pulses counted during T (seconds) from the previous routine to the current routine. ) is stored as vehicle speed V, and on the other hand,
The value of N is reset to zero and pulse counting begins again until the next routine. Then step
Proceeding to S3, it is determined whether V = 0, that is, whether pulses were counted during T seconds from the previous routine to the current interrupt processing routine, and V =
When the value is 0, the actual vehicle speed is also zero, so the process proceeds to step S4 and the value of V (ie, "zero") is input to the vehicle speed signal SPD for control information in the controller. this
When the SPD becomes zero, the above-mentioned initial setting of the rear wheels becomes possible. From step S4, the process advances to step S10 to complete the interrupt process and prepare for the next process.

On the other hand, when V=0, that is, when the vehicle is running, it is determined whether step SPD=0. Since hysteresis processing is performed in this control, the vehicle speed signal SPD for control may be zero even if the vehicle speed fluctuates to some extent, but in this case, the process proceeds to step S4 and the value of V is input to SPD. As a result, even if SPD=0, as long as the actual vehicle speed is not zero, the value of SPD will be equal to V and will not be zero. Therefore, the rear wheels are not initialized unless the actual vehicle speed is zero.
If SPD is not 0, proceed to step S6 (V-
Determine whether or not (V-SPD)≧α, and if (V-SPD)≧α, proceed to step S8, input the value of (V-α) to SPD, and then proceed to step S10 to end the process.
When (V-SPD)<α, proceed to step S8 and (V
-SPD)≦-α, determine whether (V-SPD)≦-
When α, input the value of (V-SPD) to SPD, proceed to step S10, end the process, and input (V-SPD).
>α, the process directly advances to step S10 and ends the process. The SPD value at this time is stored and used as is for the next interrupt processing, so
If this vehicle speed processing flow is interrupted every T seconds, the current vehicle speed change will be (±α) with respect to the control vehicle speed signal SPD used in the previous interrupt processing.
As long as it is within the range, the SPD value is used as is for control purposes, and only when the vehicle speed change exceeds (±α) is the SPD value corrected so that it approaches the actual vehicle speed. That is, the signal from the vehicle speed sensor is subjected to hysteresis processing with a width of (±α) as described above.

Note that the present invention is not limited to a four-wheel steering system in which a rear wheel steering mechanism and a steering mechanism are mechanically connected as in the above-described embodiments, but also includes an electromagnetic actuator that electrically controls the rear wheel steering mechanism by a controller. It can also be applied to a type of four-wheel steering system that is directly driven. In this case, a signal from a sensor that detects the steering angle of the front wheels is also input to the controller.

(Effects of the Invention) As explained above, according to the present invention, the control vehicle speed signal input to the controller that controls four-wheel steering based on at least the vehicle speed is a signal from the vehicle speed sensor processed with hysteresis of a predetermined width. Therefore, stable control can be performed without being affected by small fluctuations in vehicle speed while driving.

[Brief explanation of the drawing]

FIG. 1 shows a four-wheel steering system for a vehicle according to the present invention.
A schematic diagram showing an example; FIG. 2 is a schematic plan view of the rear wheel steering mechanism in FIG. 1; FIG. 3 is a graph showing the relationship between the steering ratio and speed controlled by the four-wheel steering device in FIG. 1; FIG. 4 is a flowchart showing a vehicle speed processing control routine by the four-wheel steering system shown in FIG. DESCRIPTION OF SYMBOLS 1...Steering wheel, 9...Power transmission shaft, 10...Variable steering ratio rear wheel steering mechanism, 1
2...bevel gear, 22...pendulum arm, 29...
...Step motor, 31...Controller.

Claims (1)

[Scope of Claims] 1. A four-wheel steering device for a vehicle configured to steer rear wheels in accordance with steering of front wheels, the rear wheel steering being based on a front wheel steering angle determined at least in accordance with vehicle speed. A controller is provided that issues a command signal to the rear wheel steering mechanism to steer the rear wheels based on the angle ratio, and the vehicle speed signal input to the controller is a signal issued by a vehicle speed sensor that detects the vehicle speed. A four-wheel steering system for a vehicle, characterized in that the signal is input through a signal processing section that performs hysteresis processing of a predetermined width.